This invention relates to a transfer line exchanger inlet cone for connecting the process gas outlet of a hydrocarbon cracking heater with the inlet of a transfer line heat exchanger. In particular, it relates to an improved transfer line exchanger inlet cone and to methods of making the same.
The pyrolysis of hydrocarbons to produce desired olefins and diolefins is highly endothermic. Process temperatures are usually high, ranging from 1300.degree. to 1600.degree. F., with the pressure normally close to atmospheric and residence time preferably short, so as to inhibit the undesirable formation of coke particles. Quench and heat recovery equipment is provided downstream from the heater in the pyrolysis reactor system to effect cooling of the reaction products from the cracking temperature, and to thereby inhibit additional secondary reactions which have an adverse affect on yield and lead to coke formation. The hydrocarbon cracking heater may be a conventional furnace comprising a row of vertical tubes with process gas therein which is heated externally to between 1300.degree. and 1600.degree. F. All the gas from the tubes is collected and passes through the transfer line exchanger inlet cone to the transfer line heat exchanger. The transfer line heat exchanger, which is normally installed in the vertical position above the inlet cone, comprises many small diameter tubes through which the process gas flows. Shrouding these small tubes is a jacket which contains water. The hot process gas is cooled by conduction through the tube walls to the water. The water is elevated thereby to boiling temperature, and the resulting steam can be used for power requirements in the plant.
Occasionally, tube failure will occur in the transfer line heat exchanger, resulting in water leakage into the tubes due to the water being at a much higher pressure than the gas. The water will then flow down until it impinges upon the interior of the inlet cone. Complete vaporization does not occur due to the amount of water flowing down and in some cases, due to the relatively short distance the water must travel to reach the inlet cone. In general, inlet cones are made of metal casting or fabricated metal. Cones of this type will fail by cracking when suddenly quenched by a water leak of the aforementioned type. The crack may allow the process gas to escape to the atmosphere where it will burn. This presents a potential safety hazard as personnel may be burned by the hot gas leakage. Under these circumstances, the furnace must be shut down, which will adversely affect plant production. If the inlet cone cannot be repaired, for instance by welding, then it must be replaced resulting in equipment loss. These problems may be alleviated somewhat by internally lining the inlet cones with insulation, for example, refractory. However, it is still possible for the inlet cone to crack due to water seepage if there is a flaw in the insulation or refractory lining.
It is therefore desirable to define a repair procedure for cracked inlet cones which are incapable of repair by welding and thus, normally discarded. It is also desirable to redesign the inlet cone as a preventative measure so as to inhibit interruption of furnace runs by an inlet cone failure.
Attention is drawn to the following, related U.S. Pat. Nos. 3,374,832; 3,409,074; 3,416,598; 3,443,631; 3,449,212; and 3,525,389. None of these patents teaches the repair method or the improved transfer line exchanger inlet cone of the present invention.